# File: hw3_1.py
# This program the GC content of a DNA string

print 'Enter path to file containing DNA string:'

# Ask for path to file containing DNA string
# and load DNA string into memory
dna = open(raw_input(), 'U').read()

# Initialize counters
gc_counter = 0
dna_counter = 0

# Go through the DNA string
for letter in dna:
    if letter == 'g' or letter == 'G' \
        or letter == 'c' or letter == 'C':
        # Everytime a G or C base pair is encountered,
        # update gc_counter (and also global counter)
        gc_counter += 1
        dna_counter += 1
    if letter == 'a' or letter == 'A' \
        or letter == 't' or letter == 'T':
        # Everytime a A or T base pair is encountered,
        # only update the global counter
        dna_counter += 1

# Display result
print 'The GC content of the DNA string is (in %)'
print 100*(float(gc_counter) / dna_counter)
